Thermal method of recovering hydrocarbons from an underground hydrocarbon-containing formation



Nov. 5, 1968 R, W, DURH; 3,409,077

THERMAL METHOD OF RECOVERING HYDROCARBONS FROM AN UNDERGROUND HYDROCARBON-CONTAINING FORMATION Filed Sept. 29, 1966 FIG. I

I; FIG. 2

INVENTORI ROBERT W. DURIE BY: III/fw? www HIS AGENT T n gnl'b L xwrv':

United States Patent O 3,409,077 THERMAL METHOD OF RECOVERING HYDRO- CARBONS FROM AN UNDERGROUND HYDRO- CARBON-CONTAINING FORMATION Robert W. Durie, Ottawa, Ontario, Canada, assignor to Shell Oil Company, New York, N.Y., a corporation of v Delaware Filed Sept. 29, 1966, Ser. No. 582,983 Claims priority, applicgatioi Canada, Jan. 17,

4 claims. (cl. 16s-11) ABSTRACT OF THE DISCLOSURE An improved process of oil recovery comprising injecting into the formation through an injection well a hot fluid followed by injecting through the same well an oxygen-containing gas to establish a combustion front and Vdriving the oil to a production well to recover the oil.

The present invention relates to a method of recovering hydrocarbons from an underground hydrocarboncontaining formation by thermal means. In such methods, vheat is applied to the formation so as to reduce the viscosity of the hydrocarbon present in the pores of the formation to enable or improve the drainage of these yhydrocarbons to the production wells through which it is lifted to the surface.

The'heat required for the desired viscosity reduction -of the hydrocarbon can be generated in situ by injecting `oxygen-containing gas into the pores of the formatlon, which gas causes combustion of part of the hydrocarbon 'present'within the formation. The ,water vapor generated during this reaction condenses against the cold parts of thev-fo'rmation, thereby forming a condensation front 'which heats the hydrocarbon and drives it towards the production wells. A drawback of this method is the high cost of compressing the oxygen-containing gas to a suitable pressure before injecting it into the formation.

In another thermal method, a hot fluid such as hot "water, steam or another condensible gas is injected into the pores of the formation. The hot uid heats the hydrocarbon through the pores of the formation to the prorock, which losses may become unacceptable near the end of the operation, in particular if there are great distances between the individual wells.

In accordance with the present invention these disadvantages of the known methods are reduced or eliminated,

and a high recovery of hydrocarbons from a hydrocarbon-containing underground formation can be achieved at relatively low compression costs and with relatively v low heat losses.

According to the invention the method of recovering hydrocarbons from an underground, hydrocarbon-containing formation comprises the following steps:

1) ar-ranging at least two wells penetrating into the formation and communicating with the pores of the formation,

(2) injecting via one of the wells into the pores of the formation a hot fluid comprising a liquid and/ or a vapor capable of condensing in unheated parts of the formation under the conditions of operation, until a portion of the hydrocarbon has been displaced,

(3) after the cessation of such injection, injecting via the samev well an oxygen-containing gas to create conr- 3,49,77 Patented Nov. 5, 1988 lCC bustion of hydrocarbon, and either simultaneously or alternately, a liquid to recover heat absorbed by the formation from the hot tiuid, and

(4) recovering hydrocarbon through the other well during the sequence of the 'steps 2 and 3.

Preferably, the injection of the hot duid in step 2 is stopped after at least 50% of the pore volume in the part of the formation to be treated has been heated by this iluid.

The steam or other hot fluid may be -injected over the entire height of the hydrocarbon-containing formation or only at a particular level. In general, it will be preferred to inject the hot fluid at a level near the lowest part of the formation.

It is also preferred that the liquid in step 4 is injected at substantially atmospheric temperature.

If the water saturation in the pores of the lower layers of the hydrocarbon-containing formation is appreciably greater than the water rsaturation in the upper layers 0f the formation, the injection of the treating uids is preferably made 'into the layer or layers having the greatest Water saturation, provided that this water saturation is lower than 100% The invention will now be described, by Way of eX- ample, with reference to the accompanying d-rawing, in

which FIGURES l and 2 show schematically a vertical section of part of the earths crust including a hydrocarbon-containing formation, and injection and production wells. In this formation, the mobility of the hydrocarbon present in the pores is sufficiently low that it cannot be recovered in the most economic manner under influence of its own energy or by the aid of pumping equipment installed in the wells. The mobility is, furthermore, suiciently low that the application of a cold fluid drive is not economically feasible. Such hydrocarbon has hitherto been economically recoverable, if at all, by a thermal method.

FIGURE l shows the injection of the hot iiuid in step 2 of the method of the invention, whereas FIGURE 2 shows the injection of the oxygen-containing gas and the aqueous liquid in step 4 of the process.

From the surface 10 and through the layers 11 land 16 overlying the hydrocarbon-containing formation 12, there are d-rilled two wells 13 and 14, which penetrate into the formation 12. The wells are drilled and cornpleted in a manner known per se, and for sake of simplicity all details such as casing, tubing, wellhead, ce-V Vcarbons which are displaced from the formation. Al-

though the formation 12 is shown in the drawing substantially horizontal, it will be understood that the method of the invention may be applied with similar results to hydrocarbon-containing formations which are of the slanted type. The cap rock 16 which forms part of the overlying layers with 11 as well as the base rock 17, are substantially or entirely impermeable.

In accordance with the invention, there is lirst injected a hot fluid via injection well 13 into the pores of the formation, which iluid in this particular example consists of steam. This steam may be either wet, dry or superheated. If desired, a hydrocarbon may be mixed with the steam for increasing the recovery eliiciency.

The injectivity of the steam into the formation 12 may be increased in the neighborhood of the well 13, by any,

3 under this pressure into the top of the well 13. If desired, bleedwater from -a boiler supplyingthe steam may also be injected into the well 13. This has the advantage that undesirable salts are removed from the boiler without loss of heat. Undesirable salts will be removed from the boiler if wet steam is employed for injection.

The injection of steam into the formation 12 is stopped after at least 50% of the pore volume of the part of the formation to be treated has been heated. This means in practice that the `amount of injected steam is more than 3 to 10 times the pore volume measured as steamn condensate. When the part of the formation to be treated is refer-red to there is to be understood that part of the .formation arranged between the injection well(s) and the production well(s), which is, during the application ,of""the method of the invention, sufciently heated to ,if necessary with the aid of pumps or the like.

After the desired amount of steam has been injected into the pores `of the formation 12, this injection is stopped, and in place thereof compressed air or other oxygen-containing gas is pumped into the pore space of theforrnation 12 Where the temperature conditions enable spontaneous combustion to take place wherever the oxygen-containing gas comes into contact with suiciently great amounts of -hot hydrocarbon. In this way, as shown in FIGURE 2, a combustion front 19 is formed, which travels in the direction of the production well 14, and by virtue of vaporization and subsequent condensation -of water already present in the formation and of water Vcreated by the combustion, for-ms a new condensation front 20.

An aqueous liquid is simultaneously or alternately with the oxygen-containing gas injected into the formation through injection well 13, which liquid vserves as a heat carrier for transporting the heat left behind in the for- Y mation by the preceding steam injection and by the com'- buston process. The liquid, suitably. ordinary water, on

contacting the hot formation, is heated andvaporized, thereby extracting heat from the formation and transferring it to colder parts of the formation, thereby also taking part in the formation of the new condensation front 20.

`In the example as shown described with reference to the drawing, the oxygen-containing gas is air, whereas the heat carrier is primarily water.

It will be clear from the above description that the present combination of the two processes which are known per se, namely a normal hot uid drive and a ,wet in situ combustion drive (in which air and waterare simultaneously or alternately injected), constitutes very economic and efficient process for displacing hydrocarbon from the pores of hydrocarbon-containing underground formations. By first applying a steam drive to the formation, the advantage of low-energy requirements is obtained. This process is continued until the amount of heat absorbed by the treated part of the formation and adjacent layers rises to an undesirable value. At this point the manner of heat generation is changed from external heat generation by the injection of steam to in situ heat generation by the injection of air. During the in situ combustion process, the heat which was previously absorbed in the treated part of the formation is transported by the water which is injected simultaneously or alternately wit-h the air, towards the untreated pa-rt of the formation. In this manner, the reservoir of heat remainfIom the steam drive phase is utilized to heat the injected water and thereby improve the overall efficiency. Furthermore, the increasing distance between the injection well and the condensation front, which would in a simple steam drive recovery unfavorably affect the heat transport by the steam in the later stages of the recovery, has little influence on the air passing therethrough in the second phase of the' method of the invention. Since at the moment when the steam drive is replaced by the in situ combustion, the. distance between the condensation front and the production well, and consequently also the injection pressure, are considerably smaller than the corresponding distance and injection pressure would be in a simple in situ combustion process, the economics of the method of the invention yare likewise favorable.

Although in the example described with reference to the drawing only two wells have been shown for carrying out the method according to the invention, the present invention is -by no means limited thereto. Any number of wells and any type of well pattern may be used.

I claim as my invention: Y

1. An improved method of recovering oil from an underground formation containing oil in substantially non-flowable state under formation conditions, comprising the following steps:

(1) establishing injection and production Wells which penetrate the oil production zone of the formation pores and are in communication with each other;

(2) injecting through an injection well and into the production zone of the formation, steam until at least of the pore volume of the formation has ybeen steam heated and thereafter stopping the steam injection;

(3) establishing a wet in situ combustion drive by injecting through the same injection well as in step (2) 'an oxygen-containing gas and alternatelyl or simultaneously also .injecting an aqueous liquid; and,

(4) recovering the mobilized oil through a production well.

2. The method of claim 1 wherein the oxygen-containing gas is ai-r and the aqueous liquid is water.

3. The method of claim 2 wherein in step (3) the injection of air and Water is done simultaneously.

4. The method of claim 1 wherein in step (3) the water is injected after the in sit-u combustion front has been established.

, References Cited UNITED STATES PATENTSl r STEPHEN I. NOVOSAD, Piimary Examiner. 

